In internal combustion engines, valves are employed at the entry and exit ports to the cylinders in which the pistons reciprocate and provide the driving force to the crankshaft of the engine. An overhead valve engine typically has what is referred to as a "head" which forms part of the combustion chamber of the cylinder in which the piston reciprocates. Within this head are the ports which are opened and closed by the valve assemblies, to permit introduction of fuel and/or air and the expulsion of exhaust gases. Typically the valve assembly includes a valve head which moves onto and off a valve seat defined by the engine head. Extending from the valve head is a valve stem which is spring-loaded, typically in the closed position, and actuated by a standard push rod and rocker arm assembly to overcome the bias of the spring and move the valve to an open position.
The valve stem is a relatively long, cylindrical portion of the valve extending from the middle of one side of the valve head, and the valve stem moves reciprocally, and with close tolerances, through a valve guide in the engine head assembly under the action of the push rod and rocker arm assembly. The valve guide may have an internal liner or insert through which the valve stem reciprocates. Over a period of time after repeated reciprocation in the valve guide or the liner the valve stem may be caused to rock a bit during reciprocation and eventually wear away a portion of the valve guide or liner surface. As a result of this wear the valve guide often has to be repaired or the liner replaced. If this is not done, the valve may not properly seat resulting in inefficiencies in engine operation. As the rocking action becomes more pronounced due to wear, the resulting poor seating and sealing contributes to higher oil consumption due to the increase in stem-guide clearance and increased blow-by the latter being particularly on the exhaust assembly and on the inlet assembly of turbo charged engines. In addition the stresses imposed on the valve by the rocking action resulting from valve guide or insert wear may eventually cause the valve stem or some other part of the valve assembly to break and damage other parts of the engine.
In repairing valve guides to avoid these problems, the guides have typically been bored out in the cylinder head and lined with cast iron or other metal inserts. Alternatively, the engine may be equipped with such inserts and when they are worn they can be replaced. In any event to retain these inserts in place, they have been force-fitted into the bored out valve guide passageway. Tolerances of these inserts with respect to the valve stem moving therein may, however, be difficult to achieve and their wear and lubrication characteristics could be improved. However, the inserts are generally made of metal having excellent heat transfer characteristics, e.g. cast iron, which is a major consideration in the operation of the valve, as well as its longevity.
There have been approaches made to improve valve guide wear, including the use of inserts employing a metallic inner sleeve having good wear characteristics in conjunction with an outer sleeve of another metal exhibiting the desired heat conductivity. For example, in U.S. Pat. No. 4,103,662 to Kammeraad, there is disclosed an outer sleeve to fit within the valve guide and the sleeve is comprised of steel or aluminum. An inner sleeve is force-fitted into the outer sleeve and engages the valve stem during its reciprocal motion. The inner sleeve is made of the phosphor-bronze and extends the full length of the outer sleeve. The outer sleeve is roll-formed, welded and redrawn to form a solid sleeve. The inner sleeve, however, is split, and the operator typically assembles the inner sleeve within the outer sleeve before placing the entire assembly into the valve guide. The split inner sleeve once placed within the outer sleeve will expand and be retained within the outer sleeve by frictional force. After assembly, the inner sleeve is grooved for oil retention. A driving tool is employed to drive the entire assembly within the valve guide passageway in the engine head.
The aforementioned procedure although it may have some features which favor its adoption in combatting valve guide wear problems is rather complex and employs relatively thin sleeves in a multifaceted assembly procedure to eventually position the separate items in place. In addition, the advantageous heat transfer characteristics of the valve guide are diminished due to the inner sleeve forming a barrier between the valve stem and the outer sleeve and valve guide passageway along essentially their entire length.
Another prior approach to valve guide construction has been the use of a steel insert coated with a layer of Teflon to provide lubrication. When the Teflon or other plastic coating material has been employed, it generally has been extended throughout the entire length of the internal surface of the valve guide assembly and again a substantial barrier to heat transfer is presented. Moreover, the plastic surface has relatively poor wear characteristics.
A feature of the present invention is the ability to concentrate a metal or other wear-resistant surface within the valve guide in the area of the most significant wear, while maintaining for the most part the heat transfer characteristics of the valve guide assembly. Frequently, the metals of good conductivity such as cast iron from which valve inserts have been made have poorer wear characteristics, while metallic surfaces that exhibit adequate resistance to wear have poorer heat transfer properties and may be more expensive. The present invention overcomes these problems by employing a valve guide insert that is made of high strength, good heat-conducting material and has a major portion of its internal surface exposed to the valve stem, while having only a minor portion of its internal surface occupied by a wear-resistant surface in the form of a ring, e.g. up to about 30% or more of the length of the insert. The percentage of wear-resistant material can vary depending on the engine and the stem to guide to port relationships, the valve lift, lubrication, among others. In any event, a more efficient system is obtained in overcoming wear without detracting from other advantages such as good dissipation of heat. Furthermore, the invention employs relatively few parts in a unique configuration such that the valve guide insert can be placed within the valve guide passageway with a minimum of effort avoiding the complexity of systems described above.
Some embodiments of the invention which incorporate the features just described include two and three-part valve guide assemblies in which a stellite or carbide or other wear-resistant ring is carried by sleeve or valve guide insert made for example, of cast iron. In one form, the invention includes two parts where the sleeve forms a major part of the assembly and has a spring end and another end remote therefrom for carrying the wear-resistant ring. The ring is configured to be retained in place by the sleeve and is arranged in the port end of the assembly. In another arrangement there are two sleeve parts which together completely circumscribe the ring which is thereby retained. In a third embodiment, the annular recess is carved in internal surfaces at or near the port end of a single sleeve member. The ring is placed in the recess and the ring has shoulders or other retention means for maintaining it in place.
In another form of applicant's invention a portion of the internal surfaces of the valve guide sleeve is machined or, otherwise, cut-away for bonding hard, wear-resistant metal as a ring inside the sleeve. Subsequently, the ring portion of the valve guide insert is bonded to the internal surfaces. When a sufficient depth of metal has been bonded to the sleeve, the internal surface of the entire composite can then be refinished to the desired size to achieve a constant internal diameter throughout. In this manner a one piece composite assembly is achieved with the wear-resistant ring being concentrated in the area of greatest potential wear at or near the port end of the sleeve. With this assembly, unlike the Teflon coating or internal sleeves which have provided lubrication or wear resistance throughout the entire length of valve guide inserts, the internal ring and its accompanying advantageous wear characteristics can be employed only in the vicinity of maximum wear adjacent the port end of the tube. Since only a relatively small part of the internal surface of the valve guide insert is covered, the remaining portion of the insert remains exposed to the valve stem so that the heat transfer characteristics of the insert remain substantially unhindered.